100 of the World's Worst Invasive Alien Species is a list of invasive species compiled by the Global Invasive Species Database in 2014.[1] The IUCNInvasive Species Specialist Group (ISSG), which maintains the list, acknowledges that it is "very difficult to identify 100 invasive species from around the world that really are 'worse' than any others."[1]

Invasive in the Pacific, the West Indies, and parts of Central Africa. Native to Central and South America.

Notes

^Not to be confused with the animal known in North America as the elk, now recognized by many authorities as a separate species (Cervus canadensis). Also not to be confused with the animal often called "elk" in Eurasia, known in North America as the moose (Alces alces).

1.
Invasive species
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One study pointed out widely divergent perceptions of the criteria for invasive species among researchers and concerns with the subjectivity of the term invasive. Such invasive species may be either plants or animals and may disrupt by dominating a region, wilderness areas, particular habitats and this includes non-native invasive plant species labeled as exotic pest plants and invasive exotics growing in native plant communities. It has been used in this sense by government organizations as well as groups such as the International Union for Conservation of Nature. The European Union defines Invasive Alien Species as those that are, firstly, outside their natural distribution area and it is also used by land managers, botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds. The kudzu vine, Andean Pampas grass, and yellow starthistle are examples, an alternate usage broadens the term to include indigenous or native species along with non-native species, that have colonized natural areas. Deer are an example, considered to be overpopulating their native zones and adjacent suburban gardens, by some in the Northeastern, sometimes the term is used to describe a non-native or introduced species that has become widespread. However, not every introduced species has adverse effects on the environment, a nonadverse example is the common goldfish, which is found throughout the United States, but rarely achieves high densities. Scientists include species and ecosystem factors among the mechanisms that when combined, while all species compete to survive, invasive species appear to have specific traits or specific combinations of traits that allow them to outcompete native species. In some cases, the competition is about rates of growth, in other cases, species interact with each other more directly. Researchers disagree about the usefulness of traits as invasiveness markers, one study found that of a list of invasive and noninvasive species, 86% of the invasive species could be identified from the traits alone. Another study found invasive species tended to have only a subset of the presumed traits. Repeated patterns of movement, such as ships sailing to and from ports or cars driving up. An introduced species might become if it can outcompete native species for resources such as nutrients, light, physical space, water. If these species evolved under great competition or predation, then the new environment may host fewer able competitors, allowing the invader to proliferate quickly. Ecosystems in which are being used to their fullest capacity by native species can be modeled as zero-sum systems in which any gain for the invader is a loss for the native, however, such unilateral competitive superiority is not the rule. For example, barbed goatgrass was introduced to California on serpentine soils, which have low water-retention, low nutrient levels, a high magnesium/calcium ratio, and possible heavy metal toxicity. Plant populations on these soils tend to low density, but goatgrass can form dense stands on these soils. Some species, like Kalanchoe daigremontana, produce allelopathic compounds, that might have an effect on competing species

2.
International Union for Conservation of Nature
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The International Union for Conservation of Nature is an international organization working in the field of nature conservation and sustainable use of natural resources. It is involved in gathering and analysis, research, field projects, advocacy, lobbying. IUCNs mission is to influence, encourage and assist societies throughout the world to conserve nature and to ensure that any use of resources is equitable. Over the past decades, IUCN has widened its focus beyond conservation ecology and now incorporates issues related to equality, poverty alleviation. Unlike other international NGOs, IUCN does not itself aim to mobilize the public in support of nature conservation and it tries to influence the actions of governments, business and other stakeholders by providing information and advice, and through lobbying and partnerships. The organization is best known to the public for compiling and publishing the IUCN Red List. IUCN has a membership of over 1200 governmental and non-governmental organizations, some 11,000 scientists and experts participate in the work of IUCN commissions on a voluntary basis. It employs approximately 1000 full-time staff in more than 60 countries and its headquarters are in Gland, Switzerland. IUCN has observer and consultative status at the United Nations, and plays a role in the implementation of several conventions on nature conservation. It was involved in establishing the World Wide Fund for Nature, in the past, IUCN has been criticized for placing the interests of nature over those of indigenous peoples. In recent years, its relations with the business sector have caused controversy. It was previously called the International Union for Protection of Nature, establishment In 1947, the Swiss League for the Protection of Nature organised an international conference on the protection of nature in Brunnen. It is considered to be the first government-organized non-governmental organization, the initiative to set up the new organisation came from UNESCO and especially from its first Director General, the British biologist Julian Huxley. At the time of its founding IUPN was the international organisation focusing on the entire spectrum of nature conservation Early years. Its secretariat was located in Brussels and its first work program focused on saving species and habitats, increasing and applying knowledge, advancing education, promoting international agreements and promoting conservation. Providing a solid base for conservation action was the heart of all activities. IUPN and UNESCO were closely associated and they jointly organized the 1949 Conference on Protection of Nature. In preparation for this conference a list of endangered species was drawn up for the first time

3.
Common myna
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The common myna, sometimes spelled mynah, also sometimes known as Indian myna, is a member of the family Sturnidae native to Asia. An omnivorous open woodland bird with a strong instinct, the myna has adapted extremely well to urban environments. In particular, the species poses a threat to the ecosystems of Australia where it was named The Most Important Pest/Problem. The common myna is readily identified by the body, black hooded head. The bill and legs are bright yellow, there is a white patch on the outer primaries and the wing lining on the underside is white. The sexes are similar and birds are seen in pairs. The common myna obeys Glogers rule in that the birds from northwest India tend to be paler than their counterparts in South India. The range of the common myna is increasing to the extent that in 2000 the IUCN Species Survival Commission declared it among the Worlds 100 worst invasive species. The etymology of the name is as follows, Acridotheres, Greek akris, akrodos, a locust, theres. Tristis, Latin tristis, sad, gloomy, Modern Latin tristis, the common myna has two subspecies, Acridotheres tristis tristis. The subspecies melanosternus is darker than the subspecies, has half-black. The type locality of the subspecies is Puducherry, India. The calls includes croaks, squawks, chirps, clicks, whistles and growls, the common myna screeches warnings to its mate or other birds in cases of predators in proximity or when it is about to take off flying. Common mynas are popular as cage birds for their singing and speaking abilities, before sleeping in communal roosts, mynas vocalise in unison, which is known as communal noise. Common mynas are believed to pair for life and they breed through much of the year depending on the location, building their nest in a hole in a tree or wall. They breed from sea-level to 3000 m in the Himalayas, the normal clutch size is 4–6 eggs. The average size of the egg is 30.8 x 21.99 mm, the incubation period is 17 to 18 days and fledging period is 22 to 24 days. The Asian koel is sometimes brood parasitic on this species, nesting material used by mynas include twigs, roots, tow and rubbish

4.
Aedes albopictus
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It is characterized by its black-and-white-striped legs, and small black-and-white-striped body. This mosquito has become a significant pest in many communities because it associates with humans. The insect is called a tiger mosquito for its striped appearance, Aedes albopictus is capable of hosting the Zika virus and is considered a potential vector for Zika transmission among humans. In 1894, a British-Australian entomologist, Frederick A. Askew Skuse, was the first to describe the Asian tiger mosquito. Later, the species was assigned to the genus Aedes and referred to as Aedes albopictus, like the yellow fever mosquito, it belongs to the subgenus Stegomyia within the Aedes genus. This is, however, a matter, and the use of Stegomyia albopicta versus Aedes albopictus is continually debated. The Asian tiger mosquito is about 2 to 10 mm length with a striking white, the variation of the body size in adult mosquitoes depends on the density of the larval population and food supply within the breeding water. Since these circumstances are seldom optimal, the body size of adult mosquitoes is considerably smaller than 10 mm. For example, the length of the abdomen was calculated to be 2.63 mm, the wings 2.7 mm. The males are roughly 20% smaller than the females, but they are very similar. However, as in all species, the antennae of the males in comparison to the females are noticeably bushier. The maxillary palps of the males are longer than their proboscis. In addition, the tarsus of the legs of the males is more silvery. Tarsomere IV is roughly 75% silver in the males whereas the females’ is only about 60% silver, the other characteristics do not differentiate between sexes. A single silvery-white line of tight scales begins between the eyes and continues down the side of the thorax. This characteristic marking is the easiest and surest way to identify the Asian tiger mosquito, the proboscis is dark colored, the upper surface of the end segment of the palps is covered in silvery scales, and the labium does not feature a light line on its underside. The compound eyes are separated from one another. The scute, the portion of an insect’s thoracic segment, is black alongside the characteristic white midline

5.
Anopheles
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Anopheles /əˈnɒfᵻliːz/ is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised, while over 100 can transmit malaria, only 30–40 commonly transmit parasites of the genus Plasmodium. Anopheles gambiae is one of the best known, because of its predominant role in the transmission of the most dangerous malaria parasite species – Plasmodium falciparum. The name comes from the Greek αν, an, meaning not, and όφελος, óphelos, meaning profit, Anopheles mosquitoes kill about 440,000 people each year because of malaria. An association of brain tumor incidence and malaria suggests the Anopheles might transmit a virus or other agent that could cause a brain tumor, mosquitoes in other genera can also serve as vectors of disease agents, but not malaria. The ancestors of Drosophila and the mosquitoes diverged 260 million years ago, the culicine and Anopheles clades of mosquitoes diverged between 120 million years ago and 150 million years ago. The Old and New World Anopheles species subsequently diverged between 80 million years ago and 95 million years ago, Anopheles darlingi diverged from the African and Asian malaria vectors ∼100 million years ago. The Anopheles gambiae and Anopheles funestus clades diverged between 80 million years ago and 36 million years ago, a molecular study of several genes in seven species has provided additional support for an expansion of this genus during the Cretaceous period. The Anopheles genome, at 230–284 million base pairs, is comparable in size to that of Drosophila, like most culicine species, the genome is diploid with six chromosomes. The genus Anopheles is a subfamily of Anophelinae with three genera, Anopheles Meigen, Bironella Theobald and Chagasia Cruz, classification into species is based on morphological characteristics – wing spots, head anatomy, larval and pupal anatomy, chromosome structure, and more recently, on DNA sequences. The genus has been subdivided into seven subgenera based primarily on the number, the system of subgenera originated with the work of Christophers, who in 1915 described three subgenera, Anopheles, Myzomyia and Nyssorhynchus. Nyssorhynchus was first described as Lavernia by Theobald, Edwards in 1932 added the subgenus Stethomyia. Kerteszia was also described by Edwards in 1932, but then recognised as a subgrouping of Nyssorhynchus and it was elevated to subgenus status by Komp in 1937, and it is also found in the Neotropics. Two additional subgenera have since been recognised, Baimaia by Harbach et al. in 2005, two main groupings within the genus Anopheles are used, one formed by the Cellia and Anopheles subgenera and a second by Kerteszia, Lophopodomyia and Nyssorhynchus. Subgenus Stethomyia is an outlier with respect to these two taxa, within the second group, Kerteszia and Nyssorhynchus appear to be sister taxa. The number of species currently recognised within the subgenera is given here in parentheses, Anopheles, Baimaia, Cellia, Kerteszia, Lophopodomyia, Nyssorhynchus, taxonomic units between subgenus and species are not currently recognised as official zoological names. In practice, a number of levels have been introduced. The larger subgenera have been subdivided into sections and series which in turn have been divided into groups and subgroups, below subgroup but above species level is the species complex

6.
Asian long-horned beetle
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The Asian long-horned beetle, also known as the starry sky, sky beetle, or ALB, is native to eastern China, Japan, and Korea. This beetle is believed to have spread from Asia in solid wood packaging material. Adults are very large insects with bodies ranging from 1.7 to 3.9 cm in length and they are shiny black with about 20 white spots on each wing cover and long antennae conspicuously banded black and white. These beetles can fly, but generally only for short distances, the upper sections of the legs of the adults are whitish-blue. A. glabripennis can be distinguished from related species by the markings on the wing covers, Asian long-horned beetle is native to eastern Asia, primarily in eastern China, Korea, and Japan. It is invasive outside its native range, in its native range, A. glabripennis primarily infest trees maple, poplar, willow, and elm. In the United States, A. glabripennis has completed development on species of genera and also Aesculus, Albizia, birch, katsura, ash, planes. In Canada, complete development has been confirmed only on maple, birch, poplar, maple is the most commonly infested tree genus in North America, followed by elm and willow. In Europe, complete development has been recorded on maple, Aesculus, alder, birch, hornbeam, beech, ash, planes, poplar, Prunus, willow, and Sorbus. The top five host genera infested in Europe, in decreasing order, are maple, birch, willow, Aesculus, not all poplar species are equally susceptible to attack. However, it has also been eradicated from some regions within these states and provinces. Adult females lay 45–62 eggs in their lifetime by chewing a small pit through the bark of the host tree to the cambium, eggs hatch in 13–54 days depending on temperature. Eggs that have not developed enough, such as those laid in summer or early fall, will overwinter. Larvae are cylindrical and elongate and can be 50 mm long and 5.4 mm wide, larvae first create a feeding gallery in the cambial region, but more mature larvae tunnel to the heartwood as they feed. Larvae go through at least five instars over 1–2 years, which can vary due to host or temperature conditions, larvae expel frass from their tunnels near the original oviposition site. A larva can consume up to 1,000 cubic cm of wood in its lifetime, Asian long-horned beetle larvae do not pupate before they reach a critical weight, so additional larval instars can occur. Pupation usually occurs in spring at the end of the tunnel in the sapwood, eclosion occurs 12–50 days later. Adults feed on leaf petioles and can chew through bark on small branches to feed on the vascular cambium, eggs, larvae or as pupae can overwinter within the tree

7.
Arundo donax
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Arundo donax, giant cane, is a tall perennial cane growing in damp soils, either fresh or moderately saline. It is one of the species of the so-called reed. Other common names include Carrizo, Arundo, Spanish cane, Colorado river reed, wild cane, Arundo donax is native to the Mediterranean Basin and middle east Asia, and probably also parts of Africa and southern Arabian Peninsula. It forms dense stands on disturbed sites, sand dunes, in wetlands, Arundo donax generally grows to 6 metres, in ideal conditions it can exceed 10 metres, with hollow stems 2 to 3 centimetres diameter. The leaves are alternate,30 to 60 centimetres long and 2 to 6 centimetres wide with a tip, grey-green. Overall, it resembles an outsize common reed or a bamboo, Arundo donax flowers in late summer, bearing upright, feathery plumes 40 to 60 centimetres long, that are usually seedless or with seeds that are rarely fertile. Instead, it reproduces vegetatively, by underground rhizomes. The rhizomes are tough and fibrous and form knotty, spreading mats that penetrate deep into the soil up to 1 metre deep, stem and rhizome pieces less than 5 centimetres long and containing a single node readily sprouted under a variety of conditions. This vegetative growth appears to be adapted to floods, which may break up individual A. donax clumps, spreading the pieces. Arundo donax is a tall, perennial C3 grass species belongs to the subfamily Arundinoideae of the Poaceae family, the hollow stems,3 to 5 cm thick, have a cane-like appearance similar to bamboo. Mature stands can reach a height up to 8 m, stems produced during the first growing season are unbranched and photosynthetic. It is an asexually reproducing species due to seed sterility and it needs to be established by vegetative propagation, due to a lack of viable seed production. Underground it produces a network of large, but short rhizomes like bulbs. From late July the lower leaves start to dry, depending to seasonal temperature patterns, crop drying accelerates during autumn when anthesis occurs from the beginning of October to the end of November. In this phenological stage moisture contents fall significantly, in winter-time giant reed stops its growth because of low temperatures and regrowth occurs in the following springtime. In Central Europe giant reed behaves as an energy crop for the low soil temperatures. The base growth temperature reported for giant reed is 7 °C, and it has a high photosynthetic capacity, associated with absence of light saturation. Carbon dioxide exchange rates is high compared to other C3 and C4 species, under natural condition, the maximum CO2 uptake ranged between 19.8 and 36.7 µmol m−2 s−1, depending on irradiance, leaf age, and it is regulated by leaf conductance

8.
Silverleaf whitefly
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The silverleaf whitefly is one of several whiteflies that are currently important agricultural pests. The silverleaf whitefly is classified in the family Aleyrodidae, and is included in the large sub-order of insects, a review in 2011 concluded that the silverleaf whitefly is actually a species complex containing at least 24 morphologically indistinguishable species. The silverleaf whitefly thrives worldwide in tropical, subtropical, and less predominately in temperate habitats, cold temperatures kill both the adults and the larvae of the species. While the silverleaf whitefly had been known in the United States since 1896, for convenience that strain was referred to as strain B, to distinguish it from the milder infestation of the earlier known strain A. Less than a year after its identification, strain B was found to have moved to tomatoes, within five years, the silverleaf whitefly had caused over $100 million in damage to Texas and California agriculture industries. During the adult stages of the whitefly, the body expands up to 0. 8mm in length and has a snow-white color. During feeding or resting stages the whitefly adult covers its body over with its wings, when depositing eggs, the females will lay 50 to 400 eggs ranging from 0. 10mm-0. 25mm on the under part of leaves. Female whiteflies are diploid and emerge from fertilized eggs whereas male whiteflies are haploid, eggs are laid in groups, being small in size with dimensions of 0.2 mm wide and. 1mm in height. Eggs are initially whitish in color and change to a brown color towards the time of hatching within 5 to 7 days, after the egg stage, the whitefly hatchling develops through four instar stages. In the first instar, commonly called the crawler, the nymph is 0. 3mm in size, during the first instar stage the body is greenish in color and flat in body structure. The mobile whitefly nymph walks to find an area on the leaf with adequate nutrients and molts into four other instar or nymphal stages over the span of 40–50 days until it reaches adulthood. During molting, the flies shed silver skins, which are left on the leaves, during the instar phases, the whitefly maintains an opaque white appearance and does not move from the feeding site the crawler originally chooses. At the feeding site the nymphs use parts of their mouth to stab into the plant, the stage following the nymph stages is the pupal stage when the eyes become a deep red color, the body color becomes yellow, and the body structure thickens. After development is completed, adult whiteflies are approximately four times the size of the egg, with yellow bodies. Research indicates that the silverleaf whitefly likely came from India, since the whitefly is predominately associated with areas exhibiting tropical/subtropical climates, the focus shifts to how these insects attained access to crops in habitats with temperate climates. One hypothesis suggests that the transfer of plants from tropical regions may have aided in the spread of the silverleaf whiteflies to temperate environments. The ability of the whitefly to adapt to various plants facilitates the spread of plant viruses. Plants which are affected by the whitefly include, tomatoes, squash, poinsettia, cucumber, eggplants, okra, beans, other common plant damages of whitefly include, removing plant sap, breakdown of the leaves of the plant, and leaf shedding

9.
Brown tree snake
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This snake is infamous for being an invasive species responsible for devastating the majority of the native bird population in Guam. The brown tree snake preys upon birds, lizards, bats and it preys on birds and shrews in Guam. Due to the availability of prey and lack of predators in introduced habitats such as Guam, the longest recorded length of this species is one found on Guam measuring three metres. The reproductive characteristics of the tree snake have not been widely studied. The female is known to produce 4-12 oblong eggs, 42–47 millimetres long, females may produce up to two clutches per year depending upon seasonal variations in climate and prey abundance. The female deposits the eggs in hollow logs, rock crevices, populations on Guam may reproduce year round. The brown tree snake is a nocturnal, rear-fanged colubrid, possessing two small, grooved fangs at the rear of the mouth. Due to the placement of the fangs and their grooved rather than architecture, the venom is difficult to convey into a bite on a human. The snake has been reported as aggressive, but is not considered dangerous to an adult human, the venom seems to be primarily used to subdue lizards, which can be more easily positioned in the rear of the mouth for venom delivery. As a result of abundant prey resources on Guam and the absence of natural predators outside of feral pigs and mangrove monitors, brown tree snake populations reached unprecedented numbers. To minimize this threat, trained dogs are used to search, locate, numerous sightings of this species have been reported on other islands including Wake Island, Tinian, Rota, Okinawa, Diego Garcia, Hawaii, and even Texas in the continental United States. An incipient population is established on Saipan. Acetaminophen has been used to eradicate the snake on Guam. The brown tree snake is a nocturnal, arboreal species that uses visual and chemical cues in hunting in the tropical rainforest canopy and/or on the ground. It is a member of the subfamily Colubrinae, genus Boiga, the brown tree snake is generally between one and two meters in length in its native range. Variations in coloration occur in the native range, ranging from a lightly patterned brown to yellowish/green or even beige with red saddle-shaped blotches. They are rear-fanged, have a head in relation to their body. The reproductive characteristics of the tree snake are not well known

10.
Cane toad
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It is a member of the genus Rhinella, but was formerly in the genus Bufo, which includes many different true toad species found throughout Central and South America. The cane toad is a breeder, females lay single-clump spawns with thousands of eggs. Its reproductive success is partly because of feeding, it has a diet, unusual among anurans. Adults average 10–15 cm in length, the largest recorded specimen had a snout-vent length of 24 cm, the cane toad is an old species. A fossil toad from the La Venta fauna of the late Miocene of Colombia is indistinguishable from modern cane toads from northern South America and it was discovered in a floodplain deposit, which suggests the R. marina habitat preferences have long been for open areas. The cane toad has poison glands, and the tadpoles are toxic to most animals if ingested. Because of its voracious appetite, the toad has been introduced to many regions of the Pacific. The species derives its name from its use against the cane beetle. The cane toad is now considered a pest and a species in many of its introduced regions, of particular concern is its toxic skin. Cane toads are particularly dangerous to dogs, originally, the cane toads were used to eradicate pests from sugarcane, giving rise to their common name. The cane toad has many common names, including giant toad and marine toad, the former refers to its size. It was one of many species described by Linnaeus in his 18th-century work Systema Naturae, Linnaeus based the specific epithet marina on an illustration by Dutch zoologist Albertus Seba, who mistakenly believed the cane toad to inhabit both terrestrial and marine environments. Other common names include giant neotropical toad, Dominican toad, giant marine toad, in Trinidadian English, they are commonly called crapaud, the French word for toad. The genus Rhinella is considered to constitute a genus of its own. In Australia, the adults may be confused with large native frogs from the genera Limnodynastes, Cyclorana and these species can be distinguished from the cane toad by the absence of large parotoid glands behind their eyes and the lack of a ridge between the nostril and the eye. Juvenile cane toads may be confused with species of the Uperoleia genus, in the United States, the cane toad closely resembles many bufonid species. In particular, it could be confused with the southern toad, the cane toad is very large, the females are significantly longer than males, reaching an average length of 10–15 cm, with a maximum of 24 cm. Larger toads tend to be found in areas of population density

11.
Goat
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The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the family Bovidae and is related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over 300 distinct breeds of goat, Goats are one of the oldest domesticated species, and have been used for their milk, meat, hair, and skins over much of the world. In 2011, there were more than 924 million live goats around the globe, according to the UN Food, female goats are referred to as does or nannies, intact males are called bucks or billies, and juveniles of both sexes are called kids. Goat meat from animals is called kid or cabrito, while meat from older animals is known simply as goat or sometimes called chevon. To refer to the male, Old English used bucca until ousted by hegote, hegoote in the late 12th century, nanny goat originated in the 18th century and billy goat in the 19th. Goats are among the earliest animals domesticated by humans, the most recent genetic analysis confirms the archaeological evidence that the wild Bezoar ibex of the Zagros Mountains is the likely original ancestor of probably all domestic goats today. The earliest remnants of domesticated goats dating 10,000 years before present are found in Ganj Dareh in Iran. Goat remains have been found at sites in Jericho, Choga Mami Djeitun and Çayönü. Studies of DNA evidence suggests 10,000 years BP as the domestication date, historically, goat hide has been used for water and wine bottles in both traveling and transporting wine for sale. It has also used to produce parchment. Goats are considered small livestock animals, compared to animals such as cattle, camels and horses, but larger than microlivestock such as poultry, rabbits, cavies. Each recognized breed of goats has specific weight ranges, which vary from over 140 kg for bucks of larger breeds such as the Boer, within each breed, different strains or bloodlines may have different recognized sizes. At the bottom of the range are miniature breeds such as the African Pygmy. Most goats naturally have two horns, of various shapes and sizes depending on the breed, Goats have horns unless they are polled or the horns have been removed, typically soon after birth. There have been incidents of polycerate goats, although this is a genetic rarity thought to be inherited, the horns are most typically removed in commercial dairy goat herds, to reduce the injuries to humans and other goats. Unlike cattle, goats have not been bred to be reliably polled, as the genes determining sex. Breeding together two genetically polled goats results in a number of intersex individuals among the offspring, which are typically sterile

12.
Carcinus maenas
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This may also be used for crabs in the superfamily Grapsoidea. Carcinus maenas is a common littoral crab and it is known by different names around the world. In the British Isles, it is referred to as the shore crab. In North America and South Africa, it bears the name green crab or European green crab, in Australia and New Zealand, it is referred to as either the European green crab or European shore crab. C. maenas is a invasive species, listed among the 100 worlds worst alien invasive species. It is native to the north-east Atlantic Ocean and Baltic Sea and it grows to a carapace width of 90 millimetres, and feeds on a variety of molluscs, worms and small crustaceans, potentially impacting a number of fisheries. Its successful dispersion has occurred via a variety of mechanisms, such as on ships hulls, packing materials, and bivalves moved for aquaculture. C. maenas has a carapace up to 60 millimetres long and 90 mm wide, the carapace has five short teeth along the rim behind each eye, and three undulations between the eyes. The undulations, which protrude beyond the eyes, are the simplest means of distinguishing C. maenas from the closely related C. aestuarii, in C. aestuarii, the carapace lacks any bumps and extends forward beyond the eyes. Another characteristic for distinguishing the two species is the form of the first and second pleopods, which are straight and parallel in C. aestuarii, the colour of C. maenas varies greatly, from green to brown, grey or red. This variation has a component, but is largely due to local environmental factors. In particular, individuals which delay moulting become red–coloured rather than green, red individuals are stronger and more aggressive, but are less tolerant of environmental stresses, such as low salinity or hypoxia. Juvenile crabs on average display greater patterning than adults, in the Mediterranean Sea, it is replaced by the closely related species Carcinus aestuarii. In 1989, the species was found in San Francisco Bay, California, on the Pacific coast of the United States. Until 1993, it was not able to extend its range, but reached Oregon in 1997, by 2003, C. maenas had extended to South America with specimens discovered in Patagonia. In Australia, C. maenas was first reported in the late 1800s in Port Phillip Bay, Victoria and it has since spread along the south-eastern and south-western seaboards, reaching New South Wales in 1971, South Australia in 1976 and Tasmania in 1993. One specimen was found in Western Australia in 1965, but there have no further discoveries in the area since. C. maenas first reached South Africa in 1983, in the Table Docks area near Cape Town, since then, it has spread at least as far as Saldanha Bay in the north and Camps Bay in the south, over 100 kilometres apart